The present invention relates to an ink jet recording head and an ink jet recording apparatus used this head, which records characters and images on a recording medium by making ink drops eject from nozzles.
In Japanese Patent Publication No. SHO 53-12138 and Japanese Patent Application Laid-Open No. HEI 10-193587, an ink jet recording head being a drop on demand type has been disclosed. The ink jet recording head ejects ink drops from nozzles connected to pressure chambers by making pressure waves (acoustic waves) generate in the pressure chambers in which ink was filled, by using electromechanical transducers such as piezoelectric actuators as their pressure generating means.
FIG. 1 is a sectional view showing a structure of a conventional ink jet recording head. In FIG. 1, a nozzle 52 for ejecting ink drops 57, and an ink supplying path 54, which supplies ink to a pressure chamber 51 through a common ink path 53 from an ink tank (not shown), are connected to the pressure chamber 51. The bottom surface of the pressure chamber 51 is covered with a vibration plate 55, and an air damper 58 is on the common ink path 53.
In order to make the ink drops 57 eject from the nozzle 52 connected to the pressure chamber 51, mechanical displacement is generated at the vibration plate 55 by a piezoelectric actuator 56 positioned on the outside of the vibration plate 55. And pressure waves (acoustic waves) are generated in the pressure chamber 51 by changing the volume of the pressure chamber 51 by this mechanical displacement of the vibration plate 55. With these pressure waves, a part of the ink filled in the pressure chamber 51 is ejected through the nozzle 52 and the ejected ink becomes the ink drops 57. The ink drops 57 hit a recording medium such as a piece of paper and recording dots made of the ink drops 57 are formed on the paper. By repeating this process to form the recording dots based on inputted image data, characters and images are recorded on the recording medium.
At the conventional ink jet recording head mentioned above, a parameter, which decides its recording speed, is the number of nozzles. The more the number of nozzles is, the more the number of dots, which can be formed per unit time, is, and the recording speed increases. In order to meet this requirement, in a normal type ink jet recording apparatus, a multi nozzle type recording head, in which plural ink jet mechanisms (ejectors) are connected, is used. In this, the ejector is composed of the nozzle 52, the pressure chamber 51, the vibration plate 55, the piezoelectric actuator 56, and the ink supplying path 54.
FIG. 2 is a perspective view showing a basic structure of a conventional multi nozzle type ink jet recording head. In FIG. 2, an ink tank 67 is connected to a common ink path 63 through a filter 66, and plural pressure chambers 61 are connected to this common ink path 63 through ink supplying paths (not shown), and each of the plural pressure chambers 68 provides a nozzle 62. However, at this structure, in which ejectors 68 are arrayed in a one-dimensional way, the maximum number of ejectors 68 is limited to about 100 pieces, and this number cannot be increased so largely.
In Japanese Patent No. 2806386 and Japanese Patent Application Laid-Open No. HEI 10-508808, in order to increase the number of nozzles, an ink jet recording head, in which ejectors are arrayed in a two-dimensional matrix, has been disclosed. Hereinafter this ink jet recording head is referred to as a matrix head.
FIG. 3 is a perspective view showing a basic structure of a conventional matrix head for an ink jet recording head. In FIG. 3, the common ink path is composed of a common ink main path 73 and plural common ink branch paths 78, and six ejectors are connected to each of the plural common ink branch paths 78. And ink is supplied to the common ink main path 73 from an ink tank 77 through a filter 76. This matrix head structure has a great advantage to increase the number of ejectors, in this, each of the ejectors provides a pressure chamber 71, a nozzle 72, a part of the common ink branch paths 78, a vibration plate (not shown), and a piezoelectric actuator (not shown). In FIG. 3, there are six common ink branch paths 78 and six pressure chambers 71 for each of the six common ink branch paths 78, therefore the total number of ejectors is 36. For example, when the number of the common ink branch paths 78 is 26 and 10 pressure chambers 71 are disposed in each of the common ink branch paths 78, 260 ejectors can be arrayed in the matrix head. In FIG. 3, Pn shows the distance between adjacent two ejectors, and Pc shows the distance between adjacent two common ink branch paths 78.
FIG. 4 is a diagram showing a conventional matrix head for an ink jet recording head. And in FIG. 4(a), a sectional view of the conventional matrix head is shown, and in FIG. 4(b), a plane view of the conventional matrix head is shown. This structure is shown in the Japanese Patent Application Laid-Open No. HEI 10-508808. In FIG. 4, an ink path A81 shows a common ink branch path and an ink path B88 shows a common ink main path, and an ink path plate 89 is actually formed by a multi layered structure of plural plates. In FIG. 4, an ejector is composed of a nozzle 82, a pressure chamber 83, a vibration plate 87, a piezoelectric actuator 84, and an ink supplying path 85.
FIG. 5 is a sectional view showing another conventional matrix head for an ink jet recording head. In FIG. 5, in addition to the structure shown in FIG. 4, an air damper plate 99 and an air damper 98 are provided. And in FIG. 5, a common ink branch path 91, a nozzle 92, a pressure chamber 93, a piezoelectric actuator 94, an ink supplying path 95, a nozzle plate 96, and a vibration plate 97 are further shown.
At the matrix head mentioned above, in which the ejectors are arrayed in a two-dimensional matrix, there is an advantage to increase the number of nozzles (ejectors). However, in order to realize a stable ejection of ink from nozzles at an actual matrix head, the common ink path must be designed suitably. FIG. 6 is an equivalent circuit of the conventional matrix head for the ink jet recording head. As shown in FIG. 6, each of many ejectors 101 is connected to one of common ink branch paths 102, and each of the common ink branch paths 102 is connected to a common ink main path 103. Therefore, in order to prevent that pressure wave interference (crosstalk) between ejectors 101 is generated, and also to prevent that refilling time is increased, at the time when many ejectors 101 eject ink at the same time, it is necessary to obtain large acoustic capacitance at each of the common ink branch paths 102. In this, the refilling time is the time to refill ink in nozzles after ink drops were ejected from the nozzles. In FIG. 6, xe2x80x9cmxe2x80x9d shows inertance Kg/m4, xe2x80x9crxe2x80x9d shows acoustic resistance Ns/m5, xe2x80x9ccxe2x80x9d shows acoustic capacitance m5/N, and xcfx86 shows pressure Pa. Further, each of suffixes shows as follows: xe2x80x9cdxe2x80x9d shows a driving section, xe2x80x9ccxe2x80x9d shows a pressure chamber, xe2x80x9cixe2x80x9d shows an ink supplying path, xe2x80x9cnxe2x80x9d shows a nozzle, xe2x80x9cpxe2x80x9d shows a common ink branch path, and xe2x80x9cpxe2x80x2xe2x80x9d shows a common ink main path.
According to the study, when the acoustic capacitance of the common ink branch path is set to satisfy the condition cp greater than 10 cn, it is possible to prevent the crosstalk from generating and the refilling time from increasing. In this, the cp is the acoustic capacitance of the common ink branch path per one ejector, and the cn is the acoustic capacitance of one nozzle. When the diameter of the nozzle is defined as dn m, and the surface tension of ink is defined as "sgr" N/m, the cn can be approximated by an equation (1). In this, in the following equation (1), the Cn shows in =.                               c          n                =                              π            ⁢                          xe2x80x83                        ⁢                          d              n              4                                            48            ⁢            σ                                              (        1        )            
At a general ink jet recording head, the diameter of the nozzle dn is about 30 xcexcm, the surface tension of ink "sgr" is about 35 mN/m, consequently, the cn becomes a value about 1.5xc3x9710xe2x88x9218 m5/N. Therefore, it is necessary that the acoustic capacitance cp at the common ink branch path is set to be 1.5xc3x9710xe2x88x9217 m5/N or more. However, it is very difficult that this value of the acoustic capacitance is obtained at the common ink branch path.
In case that the stiffness of walls of the common ink branch path is high, the acoustic capacitance cp at the common ink branch path is shown in a following equation (2). When the volume of the common ink branch path is defined as Wp m3, and the elastic modulus of ink is xcexa Pa. In this, K is a correction factor depending on the stiffness of the walls of the common ink branch path, and its value is generally about 0.3 to 0.7.                               c          p                =                              W            p                                κ            xc3x97            K                                              (        2        )            
In case that the elastic modulus xcexa of ink is 2.2xc3x97109 Pa and K is 0.5, in order to obtain that the cp is 1.5xc3x9710xe2x88x9217 m5/N or more, it is necessary that the volume Wp of the common ink branch path is 9.9xc3x9710xe2x88x929 m3 or more. When it is assumed that the distance between adjacent two ejectors is 400 xcexcm (Pn in FIG. 3) and the height of the common ink branch path is 150 xcexcm, the requiring width of the common ink branch path becomes 260 mm or more. That is, if the walls of the common ink branch path have high stiffness, the width of the common ink branch path becomes very large. Therefore, it is impossible that the ejectors are arrayed in high density.
In order to increase the acoustic capacitance, it is necessary to provide an air damper on a part of the wall of the common ink path (refer to the air damper 58 in FIG. 1). However, there are no disclosed examples in which the air damper is attached to the common ink branch path at the matrix head. However, a multi nozzle type ink jet recording head like one shown in FIG. 2 has been disclosed in Japanese Patent Application Laid-Open No. SHO 52-49034 and Japanese Patent Application Laid-Open No. HEI 10-24568. In case that this is applied to the conventional matrix head shown in FIG. 4, the nozzle plate 86 is made of a low stiffness material and is worked as an air damper. Or as shown in FIG. 5, a structure, in which the air damper plate 99 having a part with a thin thickness is inserted and this thin thickness part is worked as the air damper 98, is used.
However, at the structure of the conventional ink jet recording head being the matrix head shown in FIGS. 4 and 5, the width of the common ink branch path cannot be set to be narrow enough. Therefore, there is a problem that the density arraying the ejectors cannot be high. This problem is explained in more detail by using numerical values.
At the structure of the conventional ink jet recording head shown in FIG. 4(a), the nozzle plate 86 also works as an air damper for the ink path A81 (common ink branch path). When the width of the air damper is defined as wd m, the thickness of the air damper is defined as td m, the length of the air damper is defined as ld m, the elastic modulus of the air damper is defined as Ed Pa, and the Poisson""s ratio of the air damper is defined as xcexdd, the acoustic capacitance of the air damper cd can be approximated by an equation (3). In this, in the following equation (3), the Cd shows in =.                               c          d                =                                            l              d                        ⁢                                          w                d                5                            ⁡                              (                                  1                  -                                      v                    d                    2                                                  )                                                          60            ⁢                          E              d                        ⁢                          t              d              3                                                          (        3        )            
It is understandable from the equation (3), the acoustic capacitance of the air damper cd is in inverse proportion to the third power of the thickness of the air damper td. Therefore, in order to increase the acoustic capacitance of the air damper cd, it is desirable that the thickness of the air damper td is made to be as thin as possible.
However, as mentioned above, at the structure of the conventional ink jet recording head shown in FIG. 4(a), the nozzle plate 86 also works as the air damper for the ink path A81 (common ink branch path). Therefore, when the thickness of the air damper is decreased, the length of the nozzle 82 is decreased. That is, there is a limit to the decrease of the thickness of the air damper. When the length of the nozzle 82 becomes short, following problems occur, that is, the ejecting direction of ink drops becomes abnormal, and the catching bubbles in the ink drops occurs. Consequently, generally, the lower limit of the length of the nozzle 82 is 20 to 50 xcexcm. Therefore, the lower limit of the thickness of the air damper becomes 20 to 50 xcexcm, and in order to make the acoustic capacitance of the common ink branch path cp be 1.5xc3x9710xe2x88x9217 m5/N or more, even when a polyimide film having low stiffness (Ed 2.0 GPa) is used for the air damper, the width of the common ink branch path needs 0.7 to 1.5 mm. Consequently, the distance between adjacent two common ink branch paths (Pc shown in FIG. 3) becomes 1 to 2 mm, and the density arraying the ejectors cannot be high.
At the conventional ink jet recording head shown in FIG. 4(a), when only the part of the air damper is made to be thin, large acoustic capacitance can be obtained at the air damper without decreasing the length of the nozzle 82, however, there is a problem that the manufacturing cost is increased largely.
Further, in case that a part, whose stiffness is low, is exposed at the surface of the head (nozzle surface), when the surface of the head is wiped, a large pressure change is generated in the ink path. Therefore, there are problems that bubbles may be caught from the nozzle and also the head itself may be broken.
Therefore, at the structure of the conventional ink jet recording head shown in FIG. 4(a), decreasing the thickness at only the part of the air damper does not become actual solution, and it is very difficult to decrease the width of the common ink branch path. Consequently, it is very difficult that the density arraying the ejectors becomes high.
And at the structure of the conventional ink jet recording head shown in FIG. 5, the number of plates, of which the head is composed, increases, and there is a problem that the manufacturing cost becomes high.
In case that the air damper plate is made of a metal material such as stainless steel using conventionally, the common ink branch path needs a quite large width. For example, when that the air damper plate is made of stainless steel having 15 xcexcm thickness (Ed=197 GPa), in order that the acoustic capacitance of the common ink branch path cp is 1.5xc3x9710xe2x88x9217 m5/N or more, the common ink branch path needs about 1.8 mm width. It is possible that a resin film is used additionally for the air damper plate, however, in this case, the number of plates to be layered further increases, and the manufacturing cost of the head increases. Therefore, at the structure shown in FIG. 5, there is a problem that it is very difficult to manufacture an ink jet recording head whose density arraying the ejectors is high with low cost.
Further, at the conventional matrix head for the ink jet recording head, there is a problem that it is difficult to obtain high dimensional preciseness. At the ink jet recording head, characteristics of the ink supplying path such as inertance and acoustic resistance are important parameters to influence ink ejecting characteristics such as the volume of ink drops and ink dropping speed. Therefore, high dimensional preciseness is required at the ink supplying path.
However, at the conventional ink jet recording head, as shown in FIG. 4(a), the ink paths are formed by adhering plural plates. Generally, etching is applied to a metal plate to form the ink supplying path, in this case, there is a problem that dispersion about xc2x15 to 10 xcexcm occurs in the width of the ink supplying path.
In case that the plates are layered by using adhesive, a part of the adhesive is stuck out in the ink paths, and there is a problem that the cross sectional area of the ink paths changes largely.
As mentioned above, at the structure of the conventional matrix head for the ink jet recording head, it is difficult that the shape of the ink supplying path has high preciseness. As a result, some dispersion occurs in the volume and the ejecting speed of ink drops that are ejected from each of the ejectors, therefore, there is a problem that the quality of the output image is deteriorated.
Further, at the conventional matrix head for the ink jet recording head, there is a problem that the ability to discharge bubbles from the pressure chamber is not high. As mentioned above, at the ink jet recording head, ink drops are ejected by the pressure waves generated in the pressure chamber. However, when bubbles remain in the pressure chamber, the pressure generating efficiency is lowered and the volume and the ejecting speed of the ink drops are decreased, and in case that the amount of the remaining bubbles is large, it becomes impossible to eject the ink drops. Therefore, at a general ink jet recording apparatus, the bubbles in the pressure chamber are removed by sucking ink from the nozzles.
However, the aspect ratio of the bottom surface of the pressure chamber at the matrix head is close to 1, and the cross sectional area of the pressure chamber is large. Consequently, it is difficult to obtain high flowing speed in the pressure chamber at the time when the ink is sucked. Especially, at the conventional matrix head shown in FIG. 4, the nozzle is positioned at the upper center part of the pressure chamber. Therefore, there is a problem that it is very difficult to discharge bubbles because the ink flow in the pressure chamber is liable to stagnate.
It is therefore an object of the present invention to provide an ink jet recording head and an ink jet recording apparatus used this head, which realizes a matrix head having high density in arraying ejectors with low manufacturing cost. Moreover, the ink jet recording head and the ink jet recording apparatus of the present invention have low dispersion at ink ejecting characteristics and are suitable for high quality recording. Furthermore, the ink jet recording head and the ink jet recording apparatus of the present invention have high ability to discharge bubbles and high reliability.
According to a first aspect of the present invention for achieving the object mentioned above, there is provided an ink jet recording head, which has plural pressure chambers, arrayed in a two-dimensional matrix and connected to plural ink supplying routes connected to plural common ink branch paths one by one through a common ink main path, and ejects ink drops from nozzles connected to the plural pressure chambers, where ink was filled through the plural ink supplying routes, one by one, by making pressure changes generate in the plural pressure chambers by using a pressure generating means. The ink jet recording head provides multi layered plates. And the multi layered plates at least include a nozzle plate for forming the nozzles, a common ink path plate for forming the common ink main path, the plural common ink branch paths, and a part of connecting paths that connect the nozzles to the plural pressure chambers one by one, an ink supplying plate for forming the ink supplying routes and a part of the connecting paths, and a pressure chamber plate for forming the plural pressure chambers. And the ink supplying plate also works as air dampers for the plural common ink branch paths.
According to a second aspect of the present invention, in the first aspect, the ink supplying plate is made of a resin film.
According to a third aspect of the present invention, in the second aspect, the thickness of the ink supplying plate is 30 xcexcm or less.
According to a fourth aspect of the present invention, in the first aspect, the ink supplying routes are holes formed in the ink supplying plate.
According to a fifth aspect of the present invention, in the first aspect, the ink supplying routes are formed by applying a laser process to the ink supplying plate.
According to a sixth aspect of the present invention, in the first aspect, the ink jet recording head further provides a connecting path plate in which a part of the connecting paths is formed and also concave parts are formed on the surface facing the plural ink common branch paths by placing the connecting path plate between the ink supplying plate and the pressure chamber plate.
According to a seventh aspect of the present invention, in the sixth aspect, the concave parts have a shape matching with a shape of the plural common ink branch paths.
According to an eighth aspect of the present invention, in the sixth aspect, each of the concave parts is connected to the outside air through a path.
According to a ninth aspect of the present invention, in the first aspect, the nozzle plate is formed by a stainless steel plate.
According to a tenth aspect of the present invention, in the first aspect, the nozzle plate is formed by a resin film.
According to an eleventh aspect of the present invention, in the tenth aspect, the nozzle plate also works as air dampers for the plural common ink branch paths.
According to a twelfth aspect of the present invention, in the first aspect, each of the plural common ink branch paths is positioned in a state that each of the plural common ink branch paths is above some of the plural pressure chambers formed in the pressure chamber plate by placing the ink supplying plate between them.
According to a thirteenth aspect of the present invention, in the twelfth aspect, the width of each of the plural common ink branch paths is wide at the place where each of the plural common ink branch paths is not above the plural pressure chambers, and is marrow at the place where each of the plural common ink branch paths is above the plural pressure chambers.
According to a fourteenth aspect of the present invention, in the first aspect, corners of each of the pressure chambers are round corners.
According to a fifteenth aspect of the present invention, in the first aspect, walls of each of the pressure chambers have a round shape by applying both sides etching to the pressure chamber plate.
According to a sixteenth aspect of the present invention, in the first aspect, walls of each of the plural common ink branch paths have a round shape by applying both sides etching to the common ink path plate.
According to a seventeenth aspect of the present invention, in the sixth aspect, walls of each of the connecting paths have a round shape by applying both sides etching to the connecting path plate.
According to an eighteenth aspect of the present invention, in the first aspect, each of the ink supplying routes is positioned at the opposite side of each of the nozzles for each of the plural pressure chambers.
According to a nineteenth aspect of the present invention, there is provided an ink jet recording head. The ink jet recording head provides a nozzle plate being a stainless steel plate, in which nozzles for ejecting ink drops are formed, a common ink path plate, in which a part of a common ink main path, plural common ink branch paths, and a part of connecting paths are formed, an ink supplying plate, in which ink supplying holes, a part of the common ink main path, and a part of the connecting paths are formed, a connecting path plate, in which a part of the main common path, a part of the connecting paths, and concave parts are formed, and a pressure chamber plate, in which plural pressure chambers, arrayed in a two-dimensional matrix, are formed. And the nozzle plate, the common ink path plate, the ink supplying plate, the connecting path plate, and the pressure chamber plate are layered from the top in the order mentioned above on a vibration plate. And ink is supplied to each of the pressure chambers through the common ink main path, each of the plural common ink branch paths, each of the ink supplying holes, and each of the connecting paths. And each of the pressure chambers ejects ink drops from each of the nozzles through each of the connecting paths by making pressure changes generate in each of the pressure chambers by a pressure generating means. And the ink supplying plate is made of a resin film whose thickness is 30 xcexcm or less and also works as air dampers for the plural common ink branch paths, the ink supplying holes are formed by a laser process. And the concave parts are formed on the surface facing the plural common ink branch paths through the ink supplying plate, on the connecting path plate, by having a shape matching with the shape of the plural common ink branch paths, and works as air dampers for the plural common ink branch paths, and the concave parts are connected to the outside air. And each of the plural common ink branch paths is positioned in a state that each of the plural common ink branch paths is above some of the plural pressure chambers formed in the pressure chamber plate by placing the ink supplying plate between them. The width of each of the plural common ink branch paths is wide at the place where each of the plural common ink branch paths is not above the plural pressure chambers, and is marrow at the place where each of the plural common ink branch paths is above the plural pressure chambers. And corners of each of the pressure chambers are round corners, and each of the ink supplying holes is positioned at the opposite side of each of the nozzles for each of the plural pressure chambers.
According to twentieth aspect of the present invention, there is provided an ink jet recording head. The ink jet recording head provides a nozzle plate being a resin film, in which nozzles for ejecting ink drops are formed, a common ink path plate, in which a part of a common ink main path, plural common ink branch paths, and a part of connecting paths are formed, an ink supplying plate, in which ink supplying holes, a part of the common ink main path, and a part of the connecting paths are formed, a connecting path plate, in which a part of the main common path, a part of the connecting paths, and concave parts are formed, and a pressure chamber plate, in which plural pressure chambers, arrayed in a two-dimensional matrix, are formed. And the nozzle plate, the common ink path plate, the ink supplying plate, the connecting path plate, and the pressure chamber plate are layered from the top in the order mentioned above on a vibration plate. Ink is supplied to each of the pressure chambers through the common ink main path, each of the plural common ink branch paths, each of the ink supplying holes, and each of the connecting paths. And each of the pressure chambers ejects ink drops from each of the nozzles through each of the connecting paths by making pressure changes generate in each of the pressure chambers by a pressure generating means. And the ink supplying plate is made of a resin film whose thickness is 30 xcexcm or less and also works as air dampers for the plural common ink branch paths. And the ink supplying holes are formed by a laser process. The concave parts are formed on the surface facing the plural common ink branch paths through the ink supplying plate, on the connecting path plate, by having a shape matching with the shape of the plural common ink branch paths, and works as air dampers for the plural common ink branch paths, and the concave parts are connected to the outside air. And the nozzle plate also works as air dampers for the plural common ink branch paths, and each of the plural common ink branch paths is positioned in a state that each of the plural common ink branch paths is above some of the plural pressure chambers formed in the pressure chamber plate by placing the ink supplying plate between them. The width of each of the plural common ink branch paths is wide at the place where each of the plural common ink branch paths is not above the plural pressure chambers, and is marrow at the place where each of the plural common ink branch paths is above the plural pressure chambers. Corners of each of the pressure chambers are round corners, walls of each of the pressure chambers have a round shape by applying both sides etching to the pressure chamber plate, walls of each of the plural common ink branch paths have a round shape by applying both sides etching to the common ink path plate and walls of each of the connecting paths have a round shape by applying both sides etching to the connecting path plate. And each of the ink supplying holes is positioned at the opposite side of each of the nozzles for each of the plural pressure chambers.
According to a twenty-first aspect of the present invention, there is provided an ink jet recording apparatus. The ink jet recording apparatus provides the ink jet recording head mentioned at the nineteenth aspect.
According to a twenty-second aspect of the present invention, there is provided an ink jet recording apparatus. The ink jet recording apparatus provides the ink jet recording head mentioned at the twentieth aspect.